Summary On the morning of 09June 1997, while manoeuvring astern before berthing at a marina pontoon, the MARSOUIN, with three persons on board, shipped seas over the stern, which caused the vessel to heel to starboard and then capsize. The vessel remained afloat after capsizing and all three persons surfaced, held on to the overturned hull, and were soon rescued uninjured. Ce rapport est galement disponible en franais. Other Factual Information The MARSOUIN is a small research vessel employed in various marine biology research projects conducted by scientists at the Institut Maurice-Lamontagne (IML). The vessel is of fibreglass (glass-reinforced plastic) construction, and a watertight well deck extends from the after end of the wheel-house to the stern, beneath which permanent foamed-in-place buoyancy is fitted. The vessel was tied up starboard side to a pontoon inside the marina at Rivire-du-Loup, while a mechanic carried out repairs to the port side outboard motor. Some wave crests occasionally shipped over the transom and were pumped overboard by the intermittent use of an electrically powered bilge pump located at the after end of the well deck. The orientation of the pontoon was such that it was aligned with the marina entrance, and the stern of the vessel was exposed to the prevailing winds and waves. Before the vessel's departure, winds of 10 to 15 knots were observed to be generally from the northwest, which generated waves with small white caps in the exposed waters of the St.Lawrence River, outside the marina. Where the water became shallower, near the entrance to the marina, the waves were reportedly shorter and steep-sided, and estimated to be approximately onemetre high and rolling directly into the marina entrance. Once the motor was repaired, the vessel headed toward the entrance of the marina to test the engines under way. As the vessel was proceeding to the more exposed marina entrance, short, steep, one-metre-high waves were encountered, and some spray was shipped over the gunwales. The pump activated automatically as the vessel was turned to resume its former berth. During the return, it was decided to berth port-side-to on the more sheltered side of the pontoon, and during the subsequent manoeuvres, the motors were put into reverse. As the vessel gathered stern way, the transom became buried in a following sea causing both motors to stall and water to be shipped over the transom. Several attempts to restart the motors from the conning position in the wheel-house were unsuccessful, and as the vessel trimmed by the stern, the well deck was soon swamped by two more waves. At about 1115, the vessel capsized to starboard. The vessel capsized so rapidly that it remained afloat in the inverted position supported by air trapped in the forecastle and the wheel-house and also by the built-in buoyancy under the well deck. The mechanic and deck-hand, who were on the well deck at the time of the capsizing, were immersed but soon surfaced and held onto the inverted hull. However, the operator experienced some difficulty in exiting the enclosed wheel-house, as she was impeded by various loosely stowed items that floated out of the forecastle, and because the doorway was partially obstructed by the mechanic as he also was abandoning the vessel from the port side of the well deck. The capsizing was witnessed from the shore, and a small boat was launched quickly from a tour boat berthed nearby. Within five minutes, all three victims were retrieved from the water and returned to shore without any apparent signs of injuries. The MARSOUIN, its gear and research equipment were subsequently recovered. The life-saving appliances on board the MARSOUIN were in excess of the regulatory requirements for small vessels of this size. No personal flotation device (PFD) was worn by anyone on board despite the strong winds and rough seas observed before departure. The rapidity of the capsizing precluded the donning of any of the life-saving equipment stowed in the forecastle. The stowage arrangements of the lifebuoy and inflatable liferaft were such that they could not float free, and both remained secured on the wheel-house top throughout the capsizing and subsequent recovery operations. On recovery, both outboard-motor control levers in the wheel-house were found to be in the fully forward drive position with the ignition/starting switch at ON. The outboard motor installation is such that the outlets of the exhaust gas back-pressure relief valves are approximately 125mm above the trimmed waterline when the vessel is at rest, and significantly more in the trough created in the wake of the transom when the vessel is moving ahead. However, deep immersion or prolonged submersion of the outlets when the vessel is going astern or is overtaken by following seas, can effectively prevent exhaust gas back-pressure relief and cause the motors to stall. As a vessel of less than 15 gross registered tons, the MARSOUIN was not required to submit stability data or be inspected for safety purposes by the Transport Canada Marine Safety. The vessel was licensed as required on 24 April 1985, prior to commencement of service with IML. None of the crew held any formal marine qualifications for small vessels nor were they required to by regulation. In the spring of 1997 the operator and deck-hand had attended a 10-day small boat safety course. The operator took charge of the MARSOUIN in May 1997, having six summers' previous experience in various capacities on this and other small boats at IML. As there are no original design and stability data available, the review of the vessel's stability characteristics was based on the results of post-casualty inclining experiments, rolling period tests and hull measurements. The results showed the fully loaded displacement on departure to have been some 2552kg, including a total deadweight of 982kg. The deadweight comprised the three persons on board, 122kg of fuel in the vessel's built-in tanks and 113kg of extra fuel oil in five portable tanks. Also, there was a research seawater storage tank and gear totalling 150kg, spare personal flotation devices (PFDs) and accumulated redundant equipment amounting to 374kg, all of which were unsecured. Other weights, such as the inflatable liferaft, navigation equipment, steel mast, rigging and other fittings, are estimated to have been approximately 228kg which, in conjunction with the deadweight on board at the time of the capsizing, show an operational displacement of approximately 1210kg more than the original lightship weight. The reduction of the mean freeboard, due specifically to extra fuel and accumulated spare gear, is estimated to have been approximately 5cm. Review of the reported loaded departure condition shows the vessel had relatively high initial intact transverse stability, with a metacentric height of 0.88m, a mean draught of 0.36m and a static trim by the stern of 1.4cm. The configuration of the transom and the height of the forward end of the motor well conform with the recommendation of the Construction Standards for Small Vessels (TP1332) and, on departure, the vessel had an effective static after freeboard of approximately 0.32m.